Dr. Joel Kaufman, study leader and professor of medicine and occupational and environmental health sciences at the University of Washington, along with Sara Adar, co-author of the study and research assistant professor at the University of Michigan School of public Health, have used digital photography to observe blood vessels in the eye and found a link between air pollution and heart disease in the process.

Up until this point, previous studies have indicated that heart disease may be linked to pollution, but the study conducted by Kaufman and Adar is the first to observe the connection between pollution and tiny blood vessels, called the microvasculature.

Kaufman and Adar found this link by digitally photographing the tiny blood vessels located in the back of our eyes. These vessels are very similar to those found in the heart, but it is much easier to photograph those that are in the eye because they can be measured without the use of anesthesia or probes.

Researchers used 4,607 participants who had no history of heart disease and were between the ages of 45 and 84. They snapped digital photos of the retina and calculated the fine particulate matter in the air of each participant's home. They performed this procedure over a two year span before the eye exam, and also measured short-term exposure by checking pollution levels the day before the eye exam.

Kaufman and Adar concluded that healthy people exposed to increased levels of air pollution had "narrower retinal arterioles." The pollution levels throughout the study were, for the most part, below the EPA's acceptable level, but the tiny blood vessels still narrowed by 1/100th of a human hair. This may not seem like much, but researchers warn that this is enough to indicate a higher risk of heart disease. If all microvasculature in the body were affected the same way, it could lead to severe health consequences like a stroke or heart attack.

When comparing short-term with long-term exposure, the study shows that participants with short-term exposure to pollution had the microvascular blood vessels of a person that is three years older while long-term exposure left participants with microvascular blood vessels of a person seven years older. According to Adar, this type of change would mean a three percent increase of heart disease risk for women who live in polluted areas as opposed to cleaner ones. Adar did not note what the percentage of increased risk for men would be.

"The fact that this study identified a relationship between microvascular width and airpollution exposures provides a strong potential link between the epidemiological observations of more cardiovascular events like fatal heart attacks with higher pollution exposures and a verifiable biological mechanism," said Kaufman.

Kaufman and Adar are continuing to study the effects over time in this same group of participants. They are looking to see if air pollution causes changes in vessel diameters over time in order to provide more evidence that air pollution causes the narrowing of the tiny blood vessels, thus proving that it is linked to heart disease.